Prevalence of Quinolones Resistant Staphylococcus Aureus in Clinical Isolate

Prevalence of Quinolones Resistant Staphylococcus Aureus in Clinical Isolate

Staphylococcus aureus is a gram positive, catalase positive coagulase positive, non motile coccus bacterium that causes varieties of human infection and is major cause of mild skin infection to more serious and invasive infection including septicaemia, pneumonia, endocarditis, deep seated abscesses and toxic shock syndrome (Tenover et al ., 2000). This pathogenic staphylococci often haemolyse blood, coagulate plasma and produce a variety of extra-cellular enzymes and toxins. It is known that the most common type of food poisoning is caused by a heat-stable staphylococcal entertoxins. Staphylococci rapidly develop resistance to many antimicrobial agents and presents different therapeutic problem (Jawetz et al., 2001).

This occurs as a results of man’s strategies towards preventing and treating the disease causes by staphylococcus aureus through the administration of antibiotics.

However, the phenomena known as resistance were actually increases as new antibiotics are being discovered (WHO, 2003).

The genus staphylococcus has over 35 species. But three main species of clinical important are staphylococcus aureus, staphylococcus saprophyticus and staphylococcus epidermidis. Staphylococcus aureus is coagulase positive which distinguished it from the other species. Staphylococcus aureus happens to be the major pathogen for human’s infection ranging in severity from food poisoning, boils, cellusites, folliculitis, furnncle scalded skin syndrome, abscesses and impetigo to the life threating disease such as endocarditis, toxic shock syndrome, osteuyelitis, meningitis, pneumonia and septicaemia occur during one’s life time as a result of some staphylococcus aureus infection (Geo et al., 2007).

Its occurrence is from the skin, soft tissue, respiratory, bone, joint endovascular to wound infections. It is one of the common microorganisms that causes musoconial infection which usually occurred after some surgical infected wound (Ray and Ryan, 2004).

The organism grows well mostly on some bacteriological media under certain conditions such as acrobic and microacrophillic conditions the organisms grows most at 370C but from pigments at room temperature (200C – 250C). this organism normally forms gray to deep golden yellow colonies and also ferments mountol and haemolyses red blood cells which other species do not.

About 80 -90% of staphylococcus aureus strain contain plasmids that degrades almost all the penicillins while some strain of staphylococcus aureus where resistant to the β-lactemase resistant penicillins such as methicillin and oxacillin, by the virtue of rearrangement in the penicillin binding protein in their cell membrane (Topley and Wison, 1986)

Objectives

To assess the prevalence of staphylococcus aureus resistance to quinolones

To outline the risk factors

To characterize the species

To provide useful information on the global surveillance of this pathogen.

 

CHAPTER TWO

LITERATURE REVIEW

The organism staphylococcus aureus bacterium happened to be discovered in the 1880 and was first identifies in 1880 by a surgeon, Alexander Ogston who discovered that the majority of abscesses he studies which were warm when touched and inflamed were as a result of infection by this organism.

Rosenbauch was probably the first to studies their characteristic in the laboratory, he first classified staphylococcus in 1884.

The shape of their cells was described to be cocci by Ogten four years earlier. Rosenbauch adopted and established this name to accommodate the cluster forming cocci. This shape is based on the ability of the cell to divide in more than one plane to formirregular clusters of cells this unique morphology is responsible for the generic name for these organisms (Tenover et al., 2000).

The name staphylococcus was derived from the Greek known “staphyle”. “bunch of grape” and “coccus” “a grain berry”. In addition to their morphology and ability of dividing in more than one plane, the staphylococci are grouped taximonically with related organism by virtue of being fram positive and catalase positive bacterium two types of colonies were known to be formed on solid media by Rosenbauch islates; distinguished from each other solely by colour one type formed a yellow pigment (staphylococcus aureus) and the other appears while (non-aureus).

HABITAT

Staphylococci are associated with skin naturally, skin glands and mucocus membranes. It gorws rapidly on either aerobic or anaerobic conditions and carried by its host for long period of time without any event of clinical manifestation (CDC, 1996).

Staphylococcus aureus can also be isolated from a different environmental sources such as soil, water, animal products like cheese, egg, meat sewage and formites. Nevertheless is likely that the primary source of the strains are animals and human (Wilson et al ., 1986).

These strain may actually occur as a commensal on human skin nose often about a third of the whole population (White et al.,  2002). And it also occurs in the throat less common. Actually staphylococcus aureus under these condition does not always indicate infection and therefore does not always required treatment (but treatment may actually occur).

Staphylococcus aureus can survive for some hours on a dry environmental surfaces (Kluytmous et al., 1997).

TRANSMISSION

Generally, staphylococci are found commonly on human flora. Straphylococcus aureus is mostly found in the vagina of about 4-5% of women, this predisposes them to toxic shock syndromes. Additional sources of staphylococcus by lesions and shedding from human lesions (Jawetz et al 2011).

The organism is transmitted primarily through person contact directly commonly through the hands of health care officers. The staphylococci that are associated with infection in human are colonizers of various skin and mucosal surfaces. Because the carrier state is common among the human population, infections are frequently acquired when the colonizing strain gain entrance to a normally sterile site as a result of trauma or abrasion to the skin or mucosal surface. However, the traumatic event that allows entry of the organism often may be so minor that it goes unnoticed.

Staphylococci are also transmitted from one individual to another. Upon the transmission, the organisms may established as a part of the recipient’s normal flora and later be introduced to sterile sites by trauma or invasive procedure. Alternatively, the organism may be directly introduced into normally sterile site, such as by a surgeon or nurse during surgery. Person – to – person spread of staphylococci, particularly those that have acquired antimicrobial resistance, most notably occurs in hospitals and presents substantial infection control problems. Moreover, recently serious staphylococcus aureus infections have been encountered in the community setting as well (Bailey et al., 2007).

PATHOGENESIS

Staphylococcus aureus is an important pathogen in human infection and is implicated in wide variety of infections from mild skin infection such as pimples, boils, cellulites, furuncles carbuncles, scalded skin syndrome to life threatening one such as meningitis, osteomyelitis, endocarditis and septicaemia

Staphylococcus aureus is the most virulent species of the staphylococci encountered. A wide spectrum of factors not all which are completely understood, contribute to this organism’s ability to cause infection and disease. Several toxins and enzymes medicate tissue invasion and survived at the infection site. Elaboration of these factors is chiefly responsible for the various skin wound and deep tissue infections commonly caused by staphylococcus aureus. Many of these infections can rapidly become life threatening if not treated and managed appropriately. Localized skin infections may involve in hair follicles (i.e. foliculitis) and spread deeper to cause boils (i.e. furuncles). More serious infection result when the furuncles coalesce to carbuncles. Impetigo, the staphylococcus aureus skin infection that involves the epidermis is typified by the production of vesicles that rupture and crust over. Regardless of the initial site of infection, the invasive nature of this organism always presents a threat for deeper tissue invasion, bacteriaemia and spread to one or more internal organs including the respiratory tract. Furthermore, these serious infections have emerged more frequently among non-hospitalized patients and are associated with strains that produce the panton valentive leukocidin (PVL) toxin. Also worrisome is that these serivous “community associated” infection are frequently mediated by methicillin resistant staphylococcus aureus community acquired (MRSA or CAMRSA). (Bailey et al., 2007).

PATHOGENIC FACTORS

The pathogenicity of staphylococcus aerars depends on its ability to multiply and spread widely

The production of mainly extracellular substances toxins and enzymes these substance include:- Extoxin, leucocidin, Enterotoxin, Coagulate, Deoxyribonulease (DNASE), Hyaluronidase, staphylokinase, Beta-lactamuse, Exfoliatin, Catalase and Toxic shock syndrome

EXOTIXIN

A thermolabile mixture that contains several haemolysins that destroy red blood cells and platelets. The β-toxin is a heterogeneous protein that act on a broad spectrum of eukaryotic cell membranes. The toxin is a potent haemolysin. The β-toxin degrades spyingomyelin and therefore is a toxic for many kinds of cells including human red bloods cells. The toxin is heterogenous and dissociate into submits of nonionic detergents. It disrupts biologic membranes and may have a role in staphylococcus aureus diarrhea diseases (Geo et al., 2007)

COAGULASE AND CUMPING FACTOR

Staphylococcus aureus produces on enzyme coagulase, which clots fibrinogen in plasma to form fibrin. This property was first described by 10ch in the 1903, and confirmed by much in the 1908. this demonstration of coagulase is the best single test to identify a pathogenic staphylococcus aureus.

2.4.3   LEUCOCIDIN

This is a soluble substance that kills exposed white blood cells it is heat labile and acts seductively on leukocytes. The toxin was first described by paton and valentine in the year 1932. apart from destroying leukocytes, leucoculin also causes dermonecrosis.

ENTEROTIXIN

A soluble material that is produced by about 30 to 50% of strains of staphylococcus aureus. It is a protein that can withstand boiling for about 30 minutes. Staphylococcus aureus grows and forms the toxin in the food stuff and causes vomiting and diarrhea when such food is ingested. The toxin acts on the central nervous system (in the vomit centre) and not like other enterotoxins, on the ingestine epithelium. There are four distinct antigen group A,B,C, and D of these enterotoxins (Waldnogel 2000).

DEOXTRIBOUNCELASE (DNAse)

Staphylococcus aureus produces this enzyme which is capable of destroying deoxyribonucleic acid (DNA)

HYALURONIDASE

This is a spreading factor that aids the staphylococcus aureus to invade the tissue.

STAPHYLOKINASE

This is an enzyme produced by staphylococcus aureus that casues fibrinolysis. It digest fibrin by means of staphylokinase, which activates plasminogen in the plasma to plasmin.

CATALASE

Staphylococci produce catalase which converts hydrogen peroxide into water oxygen. The catalase test differentiates the staphylococci which are positive from streptococci which are negative.

TOXIC SHOCK SYNDROME TOXIN (TSST)

Most staphylococcus aureus strain isolated from patients with toxic shock syndrome produced a toxin called toxic shock syndrome toxin (TSST-1). TSST-1 is the profotypical super antigen. TSST-1 bind to MHC class II molecules, yelding T- cell stimulation, which promotes the protean manifestations of the TSST. The toxin is associated with fever, shock, including a desquamative skin rash (Jawetz and Levison 2001)

SUSCEPTIBILITY TO ANTIBIOTICS

An antimicrobial agent called penisullin G was the first antibiotic used in medical treatment. Penicillin is a metabolic product of muld penicillium notutum. Its structure includes a β-lacetam ring with five member ring which is active against staphylococci.

Cephalosporins like cephalexin, cefuroxin and cefotaxine are all active agint gram positive cocci including staphylococci. Glycopeptides like rancomycin and tei-plowin are active against staphylococci. AMINOGLYCOSIDES such as Gentamycin and streptomycin, are broad spectrum antibiotic that is active to staphylococci macrocides, tetracyelines and quinolones are all inclusive (Ger et al., 2007).tolerance may result from failure of the drugs to inactivate the inhibitors of autolytic enzymes that degrade the organism. Because of the frequency of drug resistance strains, staphylococcal isolates have to undergone a test for antimicrobial resistance to help in the drug of choice.

BACTERIAL RESISTANCE TO ANTIBIOTICS

Bacteria have proved adapt by developing resistance to new antimicrobial agents. There are a number of ways in which bacteria can become resistant. Most of the early studies of bacterial resistance focused on single-step mutational events of chromosomal origin. Resistance to the early sulphonamide for example the result of a single amino acid change in the enzyme pteridine synthase that caused sulformide to build, loss well than para-aminobenzonic acid, similarly, a single step mutation that altered a ribosomal protein conferred resistance to stepromycin (Arthur, 1993). In the late 1950s, Japanese workers found that enteric bacteria such as shigella dyesentaries had become resistance not only to sulformides but also to the tetracycline and chloramphenicol. This resistance was not due to a chromosomal change, but rather to the presence of extra chromosomal DNA that was transmissible plasmid mediated resistance.

Bacteria also contain transposons which can insert themselves into plasmid and the chromosomes. From an epidemiological view point, plasmid mediated resistance is the most important type, since it is transmissible, is usually highly stable confers resistance to many different classes of antibiotics. Simultaneously and often is associated with other characteristic enable micro organisms to colonize and invade a susceptible host (Murray 1991).

ACQUISION OF BACTERIAL RESISTANCE

This process can be grouped into three

A.           Intrinsic resistance. These are usually related to structural features of the organisms and are determined by chromosomal genes.

B.           Mutation resistance: It is usually result from a chromosomal mutation that render the bacterium unable to interact with antibiotics

C.           Acquisition of resistance gene: here is mostly referred to plasmind-mediated (Bone et al., 1991).

FEATURES OF BACTERIAL RESISTANCE

Resistance makes an infection more difficult to treat. All antimicrobial agents have the potential to select drug resistance subpopulations of micro organism. With the wide spread use of antimicrobials, the prevalence of resistance to the new drugs has increased. Thus given sufficient time and drug use antibiotic resistance will emerge (WHO, 2002).

MECHANISM OF BACTERIAL RESISTANCE

The mechanisms of bacterial resistance according to (Virella et al., 1996). Includes

Enzymatic motivation of antibacterial agents: beta-lactamases hydrolyze the beta-lactam ring of penicillin G and many of the semi synthetic penicillin.  In gram positive bacteria, beta-lactamase destroys the beta-lactam antibacterial in the extra cellular environment, and as a consequence of the concentration of active drug in the extracellular environment foil.  Resistance is a population phenoment; a large inoculum of organism is much more resistance than a small one. The beta-lactamase gene is inducible in the presence of the drugs, and a large amount of enzyme is produced. In Gram-negative bacterial, the outer membrane retards entry of the antibiotic into the cell and the beta-lactamase is retained within the periplasmic space. Each cell is responsible for its own than that of gram-positive bacteria. A small inocullum of bacteria may be almost as resistance as a large inoculum.

Modification of cell wall permeability: The cell wall usually is not a barrier in Gram-positive bacteria. In contrast, the cell wall of Gram-negative bacteria represent a barrier to many antibiotics particularly those that have intracytoplasmic target molecule and are hydrophilic. Porins in Gram-negative bacteria, specifically center membrane protein called porins, provides entry to many hydrophilic antibiotics with molecular molecular weight up to 650 daltons. Nutations affecting porins structure may inhibt the transport of multiple antibiotics. Lipopolysaccharride (LPS) inhibit the passage of hydrophobic antibacterial agents through cell wall. Thus rough mutants which lack polysaccharide capsules and have minimal LPS in their cell walls, are more permeable  to many antibiotics. Membrane transport appears to be responsible for resistance to tetracychine as a result of decreased in permeability into the cell.

Ø  Electron transport: The uptake of amino glycosides depends primarily on electron transport of oxygen; thus, these agents are not effective anaerobic bacterial or against facultative organisms in an anaerobic environment such as absecess. Primarily, fermentative bacteria like streptococci are also relatively resistant to amino glycosides.

The Alteration of target molecules: The target molecules may be located on the cytoplosimic membrane such as ribosome. In general, alteration of the target result in decreased affinity for the antimicrobial compound. For example, the  synthesis of an dimplorfolate reductase resistance to the effect of trimethoprin result in resistance to antibacterial agents.

Development of alternate pathway: In some cases, a mutant enzyme may be pass the synthetic block exertal by the antibiotic by using an alternative pathway.  Or even clinical significance may be the possible emergence staphylococci resistance to both methiocillin and vancomycin.

Active exclusion of Antimicrobial Agent from the Bacterial: resistance to tetracycline is medicated by the synthesis of new transport proteins that actively exclude tetracycline.

Development of tolerance: The impermeability of the outer membrane and inactivation of murein hydrolases render antibacterial agent bacterial iiostatic as opposal from bactericidal.

HISTORY OF ANTIBIOTIC RESISTANCE BY STAPHYLOCOCCUS AUEUS

The discovery of penicillinase producing staphylococci in early 1960s marked the onset of acquired resistance, followed by the development and spread of strains of staphylococcus aureus resistance to the semisynthetic penicillin, macrotides, tetracycline and other therapy for staphylococcal diseases to become a global challenge. In 1990s due to the wide spread occurance of methicillin Resistance staphylococcus aureus (MRSA); empiric therapy for staphylococcal infection was changed to vancomycin in many health care institutions. In 1997, the first strain of staphylococcus aureus with reduced susceptibility to vancomycin and teicoplainin was reported from Japan. Shortly thereafter, two additional cases from the united states were reported.

The transfer of genetic element contain the van A vancomycin resistance gene from enterococcus faccalis to staphylococcus aureus, and the consequent acquisition of resistance was demonstrated in the laboratory in 1992, which was anticipated since the recognition of vancomycin resistance enterococci in 1988 (Public Health Dispatch 2002).

USE OF QUINOLONES IN TREAT OF STAPHYLOCOCCUS AUREUS INFECTION

Nalidixic acid, first quinolone and the only one approved for use as nonfluorniated compound marketed in 1962 and still in use today. The fluoroquinolones developed at the beginning of 1980s, perfloxacin, aprofloxacin and ofcoxacin are very active against methicillin sensitive staphylococcus aureus (Ray et al., 2005).

Quinolone usages in children have been limited following the observation of anthrotoxicity in juvenile animals. These compounds are been used in paediatrics only for infections occurring in cystic fibrosis patients or as second-time treatment in cases in which other antibiotics have failed. the rates of resistance to fluoroquinolones in both community acquired and nosocomial infections occurring in adults are increasing and this phenomenon cannot be ignored when deciding on using this compounds (Gendrel et al., 2003).

2.8       MECHANISM OF ACTION, PHARMACOKINETICS AND SPECTRUM OF ATIBACTERIAL ACTIVITY

The primary target of fluoroquinolones action is the bacterial topoisomerases; a class of enzymes essentialin maintaining the bacterial DNA molecule stable and biologically active (O’Donnell et al., 2000). They strongly inhibit the type II enzymes (responsible for replication of double stranded DNA) including DNA gyrase (topoisonerase II) and topoisonerase IV. The presence of a methoxy group at position 8 in the gatifloxacin and moxifloxacin increase their affinity for DNA grase and topoisomerase IV conferring increase activity against S. aureus and also a structural advantage that decreases the likehood of emergence of resistance (O’Domnell et al., 2004).

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